Prepare for It. Like the situation above, you should go into the conversation knowing how you'll respond if your boss asks you to extend your notice. If you've landed another job offer and have already set a start date, this may not be possible__so practice sticking to your guns: "Because I have a new opportunity lined up, my last day here is firm.
Also think about your relationship with your manager. Would he or she have reason to think that you'll waste your last two weeks or distract your co_workers instead of doing what you can to make the transition seamless? If so, you may be asked to cut your two weeks short.